A range of industrial-scale chemical processes use catalysts for the reduction of organic compounds and feedstocks. Many industrial catalysts are transition metal catalysts. Second and third row transition metals are most frequently associated with high reactivity, but the high cost, scarcity, and toxicity of precious and semi-precious metals raise barriers to economically- and environmentally-sustainable large-scale chemical processes. The late first row transition metals (e.g. cobalt, nickel, iron, copper, etc.), also termed “base metals” are relatively inexpensive, abundant, and often less toxic than the heavier metals. However, base metals in general display inherently low reactivity and limited scope, features attributable in part to the small size of these elements. Nonetheless, the base metals are attractive candidates for use in catalysis, provided a suitable metal core and coordination environment can be identified.
Catalytic reduction of organic compounds is a key enabling process that sustains several major chemical industries. A broad range of commercially important reductive transformations are catalyzed by transition metals. For example, the transition-metal catalyzed reductive cleavage of polar bonds, such as C—S and C—N bonds, and hydrogenation of unsaturated functional groups, such as alkenes (to alkanes), are reductive transformations pertinent to the production of environmentally safe fuels from crude petroleum feedstocks and to the production of fine chemicals.
Current industrial processes that utilize catalytic reduction are commonly mediated by relatively expensive, relatively rare, and in some cases toxic second- and third-row transition metals. The use of rare and precious transition metals raises barriers to the economic and environmental sustainability of these industrial processes. As an example, current technologies for the upgrading of petroleum feedstocks, which include hydrodesulfurization (HDS) and hydrodenitrogenation (HDN), are energy intensive. This is due to the harsh reaction conditions required for the metal catalysts currently used for these large-scale upgrading processes. Molybdenum and tungsten catalysts, promoted by cobalt and nickel ions, such as CoMoS2 and NiWS2, generally function only at high temperature (ca. 300 to 450° C.) and under high pressure of hydrogen (ca., about 90 to 120 atm). The energy and infrastructure required to maintain such reaction conditions contributes significantly to refining costs for petroleum-based fuels and chemicals. Hence, there is a demand for inexpensive, low energy, and environmentally benign catalytic processes for industrial-scale production of fuels and commodity chemicals.
Accordingly, it would be useful to design catalysts that are both inexpensive and possess properties that are suitable for catalytic processes such as hydrodesulfurization.